Enhanced Interior Gateway Routing Protocols

Enhanced Interior Gateway Routing Protocol, also known as either EIGRP or Enhanced IGRP, is a relatively new innovation from Cisco that is based on IGRP. EIGRP shares its predecessor’s distance-vector technology, but differs greatly in its operational mechanics. Additionally, EIGRP features several important new features. EIGRP.

EIGRP supports both classless and class-based IP addresses, as well as other network protocols.Other updates were designed to reduce convergence times and improve network stability. One such Enhanced IGRP update was a new algorithm, the Diffusing Update Algorithm (DUAL), which enables EIGRP routers to determine whether a path advertised by a neighbor is looped or loop free and allows a router running EIGRP to find alternative paths without waiting for updates from other routers. This helps EIGRP networks converge, without incurring any significant risk of introducing or propagating routing loops.

 

Enhanced Interior Gateway Routing Protocol

Fig: EIGRP Sample Connections.

 

Specific Advantages of EIGRP: –

During normal, stable network operation, the only EIGRP packets exchanged between EIGRP nodes are hello packets. This simple handshake enables the EIGRP routers to know that all remains well in the network.

  • Efficient use of bandwidth during convergence

EIGRP only propagates changes to the routing table, not the entire routing table. Also, updates are advertised only after a topological change rather than on a strict, periodic basis. These updates are also only transmitted to those EIGRP routers that need to know of the change. This is known as a partial, bounded update.

  • Arbitrary route summarization

We can configure a summary aggregate address for a specified interface. If there are any more specific routes in the routing table, EIGRP will advertise the summary address out the interface with a metric equal to the minimum of all more specific routes.

  • Rapid convergence

EIGRP routers store every path they have learned to every destination in the network. Therefore, a router running EIGRP can quickly converge on an alternative route after any topological change.

  • Support for VLSM and CIDR

EIGRP supports the definition of network and host numbers on any bit boundary, per interface, for both IP addresses and subnet masks.

  • Complete independence from routed protocols

EIGRP is designed to be completely independent of routed protocols. Support for routed  protocols is via individual, protocol- specific modules. Therefore, evolution of a protocol, such as IP, won’t threaten EIGRP with obsolescence. Nor will such technological advances force a painful revision of EIGRP.

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Enhanced Interior Gateway Routing Protocol

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